1. Field of the Invention
The invention relates to an electric power storage system mounted in a vehicle.
2. Description of Related Art
Japanese Patent Application Publication No. 2013-17357 (JP 2013-17357 A) discloses a plug-in vehicle and a battery system that is capable of charging a battery with external electric power via a charger (external charging). The battery system that is disclosed in JP 2013-17357 A has a circuit configuration that allows a main battery supplying electric power to a traveling motor to be charged and an auxiliary machine battery to be charged when the external charging is performed.
According to JP 2013-17357 A, however, the main battery and an inverter or the like connected to the traveling motor should be connected to each other for the auxiliary machine battery to be charged during the external charging via the charger. In addition, a boosting circuit or the like can be disposed between the main battery and the inverter. Accordingly, when the auxiliary machine battery is charged, electric power for external charging flows through the inverter and a boosting circuit via the charger, and thus durability of these converters is reduced.
The auxiliary machine battery can also be charged with electric power for external charging via the charger prevented from flowing through the inverter and the boosting circuit. For example, another DC/DC converter for the auxiliary machine battery that is connected to another auxiliary machine battery is disposed on the charger side. In this case, however, the dedicated DC/DC converter for charging the auxiliary machine battery via the charger is provided in a state where connection between the main battery and a load is blocked, and thus the number of components increases and a physique (size) of the system as a whole including the main battery increases to cause a problem.